1. Field of the Invention
The subject matter disclosed generally relates to the field of semiconductor lasers.
2. Background Information
There are many applications for laser sources that generate laser beams in the mid-infrared range of wavelengths between 2 and 10 microns, including infrared countermeasures, environmental pollutant monitoring, spectroscopic analysis, chemical weapons defense and free-space optical communications.
The most compact, efficient, rugged and inexpensive laser sources are PN junction laser diodes, but available semiconductor materials limit them to short wavelengths in the 3 micron range and below.
Solid-state and gas lasers (for example, Holmium doped YAG, or Carbon Dioxide, respectively) exist for a few specific spectral lines in this region, but for most of the region there are no convenient and effective laser sources. Available sources such as optical parametric oscillators have serious shortcomings such as high cost, low efficiency, poor reliability and limited wavelength range.
Quantum cascade lasers are semiconductor devices that generate light over much of this spectral region, but their electrical-to-optical efficiencies are limited to only a few percent. They require significant cooling (often to cryogenic temperatures) to remove waste heat, and are not easily used outside of laboratory environments.
A PN junction source of laser radiation in this wavelength range could provide advantages such as ruggedness, low cost and high efficiency compared to existing sources and would be highly desirable.